(Unedited version)
Originally appeared in the November 2008 issue of
Tropical Fish Hobbyist Magazine

Proserpinaca is a lovely genus of aquatic perennials commonly called mermaid weeds. They're attractive in the aquarium, relatively easy to grow, have been used multiple times in the study of leaf changes in plants, were written about by Henry David Thoreau in his journals, and were even originally described by the father of modern taxonomy, Carl Linnaeus. Surprisingly with all that history and their attractiveness and ease of growth in the aquarium, they aren't commonly used and it's amazingly difficult to find much practical information on these plants.

My first encounter with Proserpinaca came in the late 1990's. The plant was purchased under the name Australian hygro. Usually this name is given to a totally different species of plant, Eusteralis stellata, even though neither plants are from the genus Hygrophila. I asked around but no one knew what the plant was, so I just kept growing it. A couple years later I purchased my first digital camera and got photos of the plant and finally was able to find someone to help me identify it as Proserpinaca palustris. I can only surmise that someone was confused about labeling the plants where I purchased this because I've never seen it listed as Australian hygro since. As I mentioned it is not from the genus Hygrophila and further more the plant is not native to Australia.

Proserpinaca is from the family Haloragaceae, more commonly know as the water milfoils. There are about 9 genus in the species world wide. Four of those are in the United States, but only 2 are native, the other 2 are represented by introduced plants, so far found only in California, from the genus Gonocarpus and Haloragis. Proserpinaca and Myriophyllum are the other members of the family in the United States. Many plant enthusiasts are familiar with plants from the genus Myriophyllum as there are several plants in that genus that are used regularly in the aquarium. There are several species of Myriophyllum that grow wild in the United States, some are native and some are introduced and considered noxious weeds.

I have seen Proserpinaca being listed in North and South America on several aquarium plant web sites, but I haven't been able to find any literature or accounts that confirm that it grows in South America. The farthest south that I could find actual accounts of the plants were in the Bahamas, Jamaica and Cuba, island countries south of Florida. It's also listed in Bermuda, in the Atlantic Ocean east of the United States. It may be that the plant is also in Central America, but at this point I can't find enough resources to verify it. In North America it seems to grow in all of the eastern United States, but it seems to be limited to those states and isn't found in the western half of the continent.

Not surprisingly Proserpinaca are found in wetland areas growing in marshes, ponds, swamps, bogs and vernal pools. It's a perennial that grows both in and out of the water. The different species of Proserpinaca are similar in appearance. They are moderately small plants that can grow up to 2 to 3 feet in the wild. The lower stems often grow roots at the nodes. Stems are decumbent meaning they creep at the base, often in water, while the upper stem grows up. The flowers are bisexual, small, and rather insignificant, forming where the leaves meet the stem. Usually only one flower forms but sometimes they are clustered. The flowers produce, one each, 3 sided, somewhat triangular seeds. The leaves of the Proserpinaca are alternate and highly variable, sometimes more so on an individual plant than between the different species. The leaves will also turn red, particularly toward the winter months, in the wild.

Currently the genus Proserpinaca seems to have 3 known and recognized species, though there are several varieties.

Proserpinaca palustris was the first of this genus that was identified by Carl Linnaeus. In fact you can see a digital image of his original notes and the specimen on The Linnean Collections at P. palustris is the most prevalent of the 3 species, and is found in most of the Eastern half of the US and Canada. It's generally accepted to have 3 natural varieties. There is also a cultivar sold in the aquarium trade. and a cultivar. The common name for P. palustris is marsh mermaidweed.

While doing research for this column I had noted that the Linnaeus was listed as having identified the plant. It made me wonder how the Swedish botanist had come across this North American plant in the 1700's. It was through the Dutch botanist, Jahann Frederik Gronovius (Feb 10, 1686 – July 10, 1762). He was a patron of Linnaeus and also had contact with John Clayton, and early Virgina settler. Clayton sent specimans to Europe to Gronovius who shared them with Linnaeus. Gronovius also wrote a book based on the plants Clayton had sent him called “Flora Virginica.” Though the book was published without Clayton's knowledge it did give him credit for his contributions.

Of the Proserpinaca, P. palustris has the most variable leaves. Submersed leaves are described as pectinate (comb like) or pectinate-pinnatifid (comb like with incisions going in less than half-way to the middle of the leaf). They look somewhat like needles. Emersed leaves are linear-lanceolate (long and narrow with a lance like, pointed shape) and serrate (leaf edges are toothed). As water levels raise and lower in the wild the plant may have alternating leaf shapes. This variability of the leaves, or heterophylly has made P. palustris a good subject for experimentation in what causes changes in leaf shape in plants.

There are 3 varieties of P. palustris. They are mostly identified by the different characteristics of their seeds. All of them have triangle shaped seeds but the corners are different. Some of the seeds corners are somewhat winged, meaning the corners are thin and elongated. The different varieties are in limited areas within the range of Proserpinaca. The varieties are P. palustris var. amblyogona, P. palustris var. crebra, and P. palustris var. palustris. There is also a commercially available cultivar from Tropica of Denmark, P. palustris “Cuba.” It's listed as originally coming from Isla de la Juventud.

P. pectinata is named for the leaves which are similar growing both above and below the water. The plant is named for the comb like growth of its leaves as pect is comb in Latin. The common name is also combleaf mermaidweed Growing naturally it may look somewhat like small firs trees or a very large moss. It's somewhat smaller than P. palustris. P. pectinata flowers from late spring through the fall. The seeds are triangular like all the Proserpinaca but have flatter sides than P. palustris with irregular ridges and angled corners.

P. pectinata is listed as occurring in these states by the USDA; Alabama, Delaware, Florida, Georgia, Kentucky, Louisiana, Massachusetts, Maryland, Maine, Michigan, Mississippi, North Carolina, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island South Carolina Tennessee and Texas and in Canada in Newfoundland, and Nova Scotia. In addition P. petinata is listed as Threatened or Endangered in several states. In Main and Rhode Island it's of special concern. In Michigan it's Endangered, and in New York it's Threatened. In Pennsylvania it's extirpated, and known from a single specimen collected in 1865.

The final species of Proserpinaca is P. intermedia. There is little available information on this species other than it is somewhat between P. palustris and P. pectinata in characteristics. Intermediate between the two hence the genus and common name, intermediate mermaidweed. This plant occurs in Alabama, Florida, Georgia, Louisiana, Massachusetts, Michigan, Mississippi, New Jersey, Pennsylvania, Rhode Island, South Carolina, Tennessee, and Virgina in the United States and in Nova Scotia in Canada.

In the aquarium I've found P. palustris to be relatively easy to grow. Not surprisingly the appearance of the plant can change depending on the conditions it's grown under. This is one of those plants that, at least for me and in my opinion, looks better in a tank without additional CO2. In the non-CO2 aquariums I've grown it in, P. palustris leaves take on the standard aquatic growth appearance. Stems are much more woody than most aquarium stemmed plants and they look similar to little pine trees. In aquariums with additional CO2 added I've found these plant leaves tend to look more like the emergent form, with a saw tooth edged leaf. Since I use yeast based CO2 on my tanks that have it, and I don't always refill them as soon as I should, I have noticed that the leaf shapes will start to change as CO2 levels go down and I get a somewhat alternating effect, similar to what occurs naturally when water levels fluctuate.

Depending on the lighting and available nutrients, the leaf color can also change. In lower or more moderate lighting the plants are dark to medium green. In higher light levels P. palustris can take on a yellow or red tint. Leaf color and shape seem to be independent, so green or red leaves can occur both on the feathery aquatic form of the leaf or the saw tooth edged emergent forms. It's often listed as preferring soft to medium hard water but I haven't had trouble growing it in my rather hard desert water. As with any plant individual conditions will affect growth rates, but compared to other aquarium stemmed plants, Proserpinaca are rather slow growers.

In the journals of Henry David Thoreau written between 1857 and 1858 he writes, “The proserpinaca leaves are very interesting in the water, so finely cut.”

It's a shame that a plant that is so attractive and easy to grow, has been know for so long and well in botanical, and naturalist circles and used for research has found so little a following in the aquarium trade. Hopefully that will change in the future and more planted aquarists will grow this interesting aquatic plant.

Welcome to the Jungle | Into The Forest | The Creepy Crawlies | A Clearing in the Thicket | Algae Eaters for the Planted Aquarium
North American Natives | Why things go wrong Pt 1 | Why things go wrong Pt 2 (Algae) | Algae Eating Shrimp | Lo-Tech Tanks
Welcome to the Fish Room | The Stemmed Plants | Mosses | A Livebearer Biotope | Planted Tank Social | The Genus Hygrophila | Cyanobacteria
Easy Plants | What I Did Last Summer | Decorations in the Planted Tank | Botany-An Introduction to Plant Biology | Botany-Anatomy of a plant
Botany-How Plants Work | Easy Rosettes | Going High-Tech | Floating Plants | Dealing with Success | Bringing the Outside In | Vallisneria
Hair Algae | Flowering Aquarium Plants Part 1 | Flowering Aquarium Plants Part 2 | Liverworts in the Aquarium | Elements of Design
Planted Aquarium Maintenance | More Mosses | Invaders | Ferns in the Aquarium | Setting up a Planted Aquarium
Seaweeds of the Pacific Northwest | Proserpinaca | Hardware for the Planted Aquarium | Rotala | Neocaridina Shrimp | Lo-tech Tank Tips

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